Schedule Mechanics & Data
Open End
An open end is an activity in the middle of a schedule with no predecessor, no successor, or both -- a logic gap that keeps it from being properly tied into the calculated network.
Definition
Every activity's early dates come from its predecessors and its late dates come from its successors; an activity missing one or both defaults to the project's own start or finish date for the missing side, producing dates and float that don't reflect its real position in the work. The first activity of a project genuinely has no predecessor and the last genuinely has no successor -- those are expected. An open end anywhere else in the network is the structural problem DCMA's logic check (Check 1) specifically targets, with a target of under 5% of incomplete activity-links missing a tie.
Example
An activity added late in a schedule revision has a predecessor tying it to earlier work, but was never given a successor -- so it carries artificially high float that has nothing to do with how much real slack exists in that part of the project.